At baseline interview 7.3% (n = 1394) of the women had type 2 diabetes, with a mean duration of 12 years
since diagnosis. Of the 1248 women with diabetes who completed the most recent questionnaire, 901 reported
recent medication for management of diabetes (294 (33%) insulin, 607 (67%) oral hypoglycaemic agents). As
expected, women with diabetes had higher prevalence of several comorbid conditions (hypertension, high
cholesterol, heart disease, obesity, depression) than women without diabetes
(), and used hormone therapy less and drank less alcohol.
On every cognitive test, mean baseline scores were lower for women with diabetes
Characteristics of women aged 70-81 years, according to type 2 diabetes. Figures are percentage of
respondents unless stated otherwise*
Mean cognitive test scores at baseline in women aged 70-81, according to type 2 diabetes. Figures are
We focused analyses on two measures of general cognitive function: the TICS and the global score (). After we adjusted for potential confounding factors, women with diabetes were at 25-35% increased odds of poor baseline score compared with women without diabetes (odds ratio 1.34, 95% confidence interval 1.14 to 1.57, for TICS and 1.26, 1.06 to 1.51, for global score). Findings were consistent when we examined mean differences in scores; the mean score for women with diabetes was lower by -0.42 points, -0.58 to -0.27 points, on the TICS and by -0.09 units, -0.12 to -0.05 units, on the global score compared with women without diabetes. Associations became stronger with longer duration of diabetes. For those with diabetes for ≥ 15 years the odds of poor cognitive performance was 50% higher than for women without diabetes (1.52, 1.15 to 1.99, and 1.49, 1.11 to 2.00, respectively).
Odds of poor performance also seemed to differ across treatment groups (). Compared with women without diabetes, we found high odds of poor performance for women with diabetes who did not report pharmaceutical treatment (1.71, 1.28 to 2.28, and 1.45, 1.04 to 2.02, respectively). Those taking insulin also had modestly increased odds of poor cognition (1.20, 0.85 to 1.70, and 1.38, 0.97 to 1.95, respectively). In the more powerful analyses of mean differences, the worst performance was among women using insulin (mean differences -0.40, -0.72 to -0.09, and -0.11, -0.18 to -0.03, respectively). In contrast, those taking oral medications had similar odds of poor cognitive performance as those without diabetes (odds ratios 1.06, 0.81 to 1.37, and 0.99, 0.74 to 1.33, respectively) and had the smallest mean difference in score (mean differences -0.35, -0.58 to -0.13, and -0.06, -0.11 to -0.01, respectively).
As cognitive impairment may be a cause rather than a consequence of not taking medications, we also examined use of medication at time of diagnosis (average of 12 years before cognitive assessment). However, results were similar: the odds ratios for poor score were 1.61, 1.19 to 2.16, and 1.43, 1.02 to 2.00, respectively, for women with diabetes who were not taking medication at diagnosis compared with women without diabetes.
In addition, as duration of diabetes, medication use, and level of control are correlated we conducted additional analyses to try to assess their independent effects. The results for duration of diabetes were largely similar after we adjusted for medication use, and results for medication use were largely unchanged after we included a term for duration in the model or stratified by duration of diabetes. For example, among women with diabetes, those not taking medication had a higher risk of poor cognitive performance on the TICS compared with those taking oral medication both in the group with duration of diabetes < 10 years (1.73, 1.01 to 2.98) and ≥ 10 years (1.90, 1.04 to 3.48). Furthermore, although we did not have detailed information on level of control (for example, data on haemoglobin A1c concentration), all results were generally unchanged when we excluded data from women with metabolic complications (for instance, those with severely uncontrolled disease).
Finally, we restricted analyses to participants who did not report any difficulty with hearing (n = 12 099) to reduce confounding by hearing status. The results were similar when we compared women with and without diabetes (1.45, 1.18 to 1.78, and 1.37, 1.10 to 1.71, respectively).
Prospective analyses of decline
Although cognitive decline was measured over just a two year period, we observed a significantly increased odds of substantial decline on the TICS (1.26, 1.03 to 1.54) for women compared with women without type 2 diabetes (). However, we observed little overall relation between diabetes and decline on the global score (1.11, 0.90 to 1.37). Similarly, mean decline was greater among women with diabetes by -0.17 points (-0.33 to -0.01) on the TICS but was comparable in the two groups on the global score (mean difference in decline -0.01, -0.04 to 0.03). In addition, qualitative relations with longer duration diabetes and use of medication were generally similar to those observed with baseline cognitive function.